High speed, high capacity optical communication systems are increasingly based upon optical networks employing dense-wavelength-division-multiplexing (DWDM) technology whereby many optical wavelength channels are transmitted along an optical fiber simultaneously.
The wavelength channels are defined in grids whereby each wavelength channel is separated by 200 GHz, 100 GHz, 50 GHz or 25 GHz from the next wavelength channel. The trend is to increase the number of channels and also to increase the bandwidth of each channel. This has led to two different extreme requirements, namely wavelength channels transmitting at 40 Gbit/s on a 100 or 50 GHz grid, and wavelength channels transmitting at 10 Gbit/s on a 50 GHz or 12.5 GHz grid. Given that there are numerous optical components such as optical sources, filters, multiplexers in the network, the wavelength accuracy of each optical component becomes increasingly important. This requirement is likely to become even more demanding as the grid sizes become even more closely packed (e.g. 12.5 GHz, 6.25 GHz or even 1 GHz) and the bandwidth efficiency becomes even higher.
Optical components not only have to be manufactured to operate at a specified wavelength, they also need to do so over wide temperature and humidity ranges and for extended periods of time. This requirement is made more difficult owing to variation of optical performance of the optical components with temperature. For example, the center wavelength of a typical fiber Bragg grating device will vary by approximately 10 pm per deg C. Thus over a 100° C. temperature variation, the wavelength will shift by approximately 1 nm corresponding to an optical frequency shift of approximately 125 GHz at 1550 nm.
There is therefore a requirement for a thermal compensation device that stabilizes the performance of optical components, compensates for thermal variations within the optical component, and is applicable for volume manufacturing processes with high yield. The thermal compensation device design is preferably hermetic.
An additional requirement is that the thermal compensation device should enable individual devices to be tuned during manufacture.
Yet a further requirement is to provide a thermal compensation device that allows multiple components to be incorporated within the same thermal compensation device and that allows each of these components to be tuned individually to its correct operating wavelength.
An aim of the present invention is to provide a thermal compensation device with improved tuneability.